Thermostatic element



Feb; '17, 1939. R. G. WALTENBERG THERMOSTATIC ELEMENT Filed May 16, 1936 My fir 00 509239 f/evm nl ATTORNEYS Patented F eh. 7, 1939 THERMOSTATIC ELEMENT Romaine G. Waltenberg, Roselle, N. 1., assllnor to The H. A. Wilson Company,

New Jersey a corporation of Application May 16, 1936, Serial No. game 4 Claim.

This invention relates to thermostatic elements, such as are commonly used for control, indicating,

and similar purposes, and is concerned more particularly with a new thermostatic bimetal which has a high rate of deflection and may be employed throughout a wide range of temperatures without substantial variation in eifectiveness. The bimetal of the invention also possesses physical characteristics which make it suitable for its intended use and it may be manufactured without difiiculty by the usual methods.

The new thermostatic couple consists of a pair of elements having wideiydiflerent coefilcients of expansion secured together face to face in any suitable manner, as by welding. The low expanding member of the combination may be of any of the usual compositions customarily employed, such, for example, as a nickel steel containing from about 35 per cent to about 42 per cent of nickel or a chromium-iron alloy containing from about 12 per cent to about per cent .of chromium. The high expanding'element is of novel composition and although this element is analloy steel containing the ordinary alloying constituents, namely, nickel, chromium, and manganese, it diifers from prior high expanding elements in that these constituents are present in proportions different from those heretofore used, and new and beneficial results are thereby obtained.

One form of embodiment of the invention is illustrated in side elevation in the single figure of the drawing in which the low expanding ele ment ID of the material above described is secured face to face to the high expanding element I l of the new composition.

In the manufacture of thermostatic elements of the type to which this'invention relates, it is the common practice at present to employ a low carbon austenitic steel as the high expanding element, and to use relatively large amounts of alloying elements so that the steel will rema n stable under ordinary conditions of use. Thus, one low carbon steelwhich is now in use for the high expandingeleme'nt of a thermostatic bimetal contains a total amount of nickel, chromium, and manganese equal to about 30 per cent of the steel. Such a steel may be readily worked and welded, but its coeflicient of expansion is not as great as is desirable for some purposes.

As a result of experiments in this field, I have found that a high expanding element suitablefor thermostatic purposes and having a higher coeflicient of expansion than that of the steel above referred to may be made by employing a less total content of alloying agents, and further, that if the alloying constituents are present in different proportions from those heretofore used, the steel is stable and has satisfactory physical characteristics. To accomplish the desired results, I employ a high carbon steel alloy with nickel, chromium, and manganese, these alloying constituents being present in varying amounts, but in a total amount less than that previously used and ranging, for example, from about 18 per cent to about 25 per cent. My' new expanding element may thus contain nickel ranging from about 15 per cent ,to

about 22 per cent, chromium ranging from about 2 per cent to about 8 per cent, manganese ranging from about 0.5 per cent to about 5 per cent, and carbon ranging from about 05 per cent to about 1 per cent, together with minor amounts of silicon and cobalt as, for example, not to exceed 0.2 per cent and'0.l per cent, respectively.

The selection of the proper amounts of the several constituents in the alloy, within the ranges above specified, depends on a number of considerations having to do with the effects of these constituents on the physical'characteristics of the final product. Nickel and manganese, for example, are important factors in converting the iron to stable condition and maintaining it in that condition, manganese being the -more effective for this purpose, but when used'intoo large amounts, imparting undesirable physical characteristics to the final product. Chromium with nickel also acts to stabilize the iron and, in addition, increases the resistance of the alloy to corrosion. A high carbon content, that is, one within the specified range, permits smaller total amounts of nickel, chromium, and manganese to be employed without loss of stability. Also, I find that if any of the four constituents, nickel, chromium, manganese, or carbon, is increased within its specified range, decreased amounts of the other constituents within their ranges are permissible.

In view of these considerations, it is to be understood that I do not recommend that in 'the new material each of the alloying constituents be present in an amount which is near either the upper limits or the lowerlimits set forth, but, for example, if an element is to be made with the nickel near the lower limit specified for that constituent, the amounts of chromium and manganese present should be in the upper portions of their ranges. If, in that situation, corrosion resistance is desirable, a greater amount of chromium and a less amount of manganese may be The corrosion resistance of the high expanding element of a'bimetal is not always important, however, since if the low expanding element consists of iron and nickel only, the corrosion resistance of that element will ordinarily be less than that of the high expanding element and will, therefore, determine the resistance of the bimetal as a whole.

Examples of compositions which embody the invention are as follows, the percentages given being approximate in each case:

Example I Per cent Nickel 18 to 20 Chromium 2 to 3 Manganese 0.5 to 3 Carbon 0.5 to 0.8

Remainder iron.

Example II Per cent Nickel 19 to 19.75 Chromium 2 to 2.5 Manganese 0.90 to 1.00 Carbon 0.5 to 0.6

Remainder iron.

Example III Per cent Nickel 19.5 Chromium 2.5 Manganese 1 Carbon 0.5

Remainder iron. Each of the compositions above set forth include small amounts of silicon and cobalt, preferably not exceeding 0.2 per cent and 0.1 per cent, respectively.

In any of the alloys made in accordance with the invention, molybdenum may be used to replace some of the nickel, manganese, or chromium. When molybdenum is used to replace the chromium, either wholly or in part, more nickel or manganese is required to produce a stable alloy. The use of molybdenum increases the strength of the element at elevated temperatures above 750 F.

A high expanding element of the new composi-.

tion is characterized by its high coefficient of thermal expansion and it is effective through a range of temperatures from about --80 F. to above 1300 F. Thus. an alloy of the analysis given in Example III has a coefficient of thermal expansion of about 10.5 x at room temperature, this coefficient increasing to about 11 x 10.- at about 600 F. A steel which has heretofore been used as the high expanding element and which contains about 12 per cent nickel, about 18 per cent chromium, and small amounts of the other elements usually found in steel, has a comcient of thermal expansion of about 9.5 x 10 at room temperature, this coefficient increasing to about 10 x 10- at about 600 F.

'Since the new alloy contains a relatively high carbon content, it is somewhat more difficult to work and weld than low carbon steels, but these dimculties are not important and do not interfere with its use in the production of thermostatic elements.

In the manufacture of bimetallic elements containing the new high expanding element disclosed,

the low expanding member may be any of the commonly used alloys, which, in general, are equivalents for the purpose. It is to be understood, therefore, that in the bimetallic elements defined in the following claims, any suitable low expanding element may be substituted for the nickel steel containing 35 percent to 42 percent nickel specified, although, when such a substitution is made, I prefer to employ an alloy in which iron predominates, such, for example, as a chrome iron alloy containing from 12 percent to 25 percent of chromium.

I claim:

1. A bimetallic thermostatic element which comprises a low expanding element made of a nickel steel in which the nickel content ranges from about 35 percent to about 42 percent and a high expanding element made of a high carbon steel consisting of carbon ranging from not less than 0.5 percent to about 1 percent, nickel ranging from about 15 percent to about 22 percent chromium ranging from about 2 percent to about 8 percent, manganese ranging from about 0.5 percent to about 5 percent, the total amount of nickel, chromium, and manganese ranging from not less than 17.5 percent to not more than 24.5 percent, small amounts of silicon and cobalt not exceeding 0.2 percent and 0.1 percent, respectively, and the remainder iron.

2. A bimetallic thermostatic element which comprises a low expanding element made of a nickel steel in which the nickel content ranges from about 35 percent to about 42 percent and a high expanding element made of a high carbon steel consisting of carbon ranging from not less than 0.5 percent to about 0.8 percent, nickel ranging from about 18 percent to about 20 percent, chromium ranging from about 2 percent to about 3 percent, manganese ranging from about 0.5 percent to about 3 percent, the total amount of the nickel, chromium, and manganese ranging from not less than 17.5 percent to not more than 24.5 percent, small amounts of silicon and cobalt not exceeding 0.2 percent and 0.1 percent, respectively, and the remainder iron.

3. A bimetallic thermostatic element which comprises a low expanding element made of a nickel steel in which the nickel content ranges from about 35 percent to 42 percent and a high expanding element made of a high carbon steel consisting of carbon ranging from not less than 0.5 percent to about 1 percent, nickel ranging from about 19 percent to about 19.75 percent, chromium ranging from about 2 percent to about 2.5 percent, manganese ranging from about 0.9 percent to about 1 percent, small amounts of silicon and cobalt not exceeding 0.2 percent and 0.1 percent, respectively, and the remainder iron.

4. A bimetallic thermostatic element which comprises a low expanding eelment made of a nickel steel in which the nickel content ranges from about 35 percent to about 42 percent and a. high expanding element made of a high carbon steel consisting of carbon in an amount from not less than 0.5 percent to about 1 percent, about 19.5 percent nickel, about 2.5 percent chromium, about 1 percent manganese, small amounts of silicon and cobalt not exceeding 0.2 percent and 0.1 percent, respectively, and the remainder iron.

ROMAINE G. WALTENBERG. 

